Biomass combined cycles based on externally fired gas turbines and organic Rankine expanders

Abstract

This article investigates the possibility to enhance the performance of a biomass organic Rankine cycle (ORC) plant by adding an externally fired gas turbine (EFGT), yielding a combined EFGT + ORC system. A typical ORC configuration is first modelled and validated on data available from an existing unit 1.5 MW reference plant. Then, different working fluids belonging to the methyl-substituted benzene series and linear methylpolysiloxanes have been evaluated for the ORC section on the basis of both thermodynamics considerations and design issues of the regenerator and the turbine. Results of the simulations of the combined cycle (CC) referred to a furnace size of about unit 9 MW, assuming a maximum GT inlet temperature of 800 °C, show a maximum efficiency of 23 per cent, obtained in the case where toluene is adopted as a working fluid for the bottoming section. This value is about 4 points per cent higher than the efficiency of the corresponding simple ORC. Finally, to conclude, some preliminary considerations are given regarding the techno-economic feasibility of the combined configuration, suggesting the need of a further investigation on the possible technological solution for the furnace which represents the main uncertainty in the resulting costs of the CC

Part-Load Performance of aWet Indirectly Fired Gas Turbine Integrated with an Organic Rankine Cycle Turbogenerator

“…This technique improves further the plant performances by decreasing the exhaust temperature of the gases released to the environment. Despite the difference in the proposed plant layouts, the selection of the optimal working fluid for the ORC turbogenerator is in accordance with the results reported in Invernizzi et al [13]. Table 1 indicates that all the organic compounds considered in this study present a relatively high flammability and toxicity.…”

“…Compared with the original configuration proposed by Invernizzi et al [13], the ORC unit is not powered directly by the heat contained in the air exiting the gas turbine module. After the expansion process, the air acts in fact as oxidant in the combustion process.…”

“…Invernizzi et al [13] proposed a first attempt to integrate an IFGT with an ORC power module. With a combustion temperature of 700…”

“…The thermal efficiency was found to be around 25% for all moisture contents of the combustible. Invernizzi et al [13] proposed the integration of IFGTs with ORC power modules. The plant was analyzed using the first principle of thermodynamics.…”

“…This paper aims at evaluating the optimal design and the part-load performance of an innovative plant consisting of a WIFGT fueled by woodchips and an ORC turbogenerator. The plant layout proposed by Invernizzi et al [13] is modified by exploiting the air exiting the gas turbine unit to oxidize the biomass in the burner and by including a dryer for the combustion of the wet woodchips. An exergy analysis is performed to identify the thermodynamic irreversibilities of the plant and the optimal design variables.…”